Clarify use of DataSource for batch apps

Closes gh-8271

Author: snicoll

spring-boot-docs/src/main/asciidoc/howto.adoc

@@ -2261,6 +2261,11 @@ your application defines, if any.
 [[howto-batch-applications]]
 == Batch applications
 
+NOTE: By default, batch applications require a `DataSource` to store job details. If you
+want to deviate from that, you'll need to implement `BatchConfigurer`, see
+{spring-batch-javadoc}/core/configuration/annotation/EnableBatchProcessing.html[The
+Javadoc of @EnableBatchProcessing] for more details.
+
 
 
 [[howto-execute-spring-batch-jobs-on-startup]]

spring-boot-docs/src/main/asciidoc/index.adoc

@@ -41,6 +41,7 @@ Phillip Webb; Dave Syer; Josh Long; Stéphane Nicoll; Rob Winch; Andy Wilkinson;
 :spring-webservices-reference: http://docs.spring.io/spring-ws/docs/{spring-webservices-docs-version}/reference/htmlsingle
 :spring-javadoc: http://docs.spring.io/spring/docs/{spring-docs-version}/javadoc-api/org/springframework
 :spring-amqp-javadoc: http://docs.spring.io/spring-amqp/docs/current/api/org/springframework/amqp
+:spring-batch-javadoc:http://docs.spring.io/spring-batch/apidocs/org/springframework/batch
 :spring-data-javadoc: http://docs.spring.io/spring-data/jpa/docs/current/api/org/springframework/data/jpa
 :spring-data-commons-javadoc: http://docs.spring.io/spring-data/commons/docs/current/api/org/springframework/data
 :spring-data-mongo-javadoc: http://docs.spring.io/spring-data/mongodb/docs/current/api/org/springframework/data/mongodb